The present invention relates to apparatus for producing helical coils of metallic wire, plastic wire or the like. More particularly, the invention relates to improvements in apparatus for producing helical wire coils which can be subdivided (for example, immediately downstream of the location of making) into discrete spiral binders of the type normally used to hold together the sheets of a steno pad, exercise book, album or an analogous stationery product by extending through perforations provided in one marginal portion of a stack of superimposed sheets consisting of paper, foil, cardboard and/or the like.
Apparatus of the above outlined character normally employ a coiling tool in the form of a driven mandrel having a conical external surface adjacent to stationary guide means which define a helical path for a length of wire that is supplied or steered into the inlet of such path by a preferably adjustable feeding device. The lead of the helical path which is defined by the guide means corresponds to or approximates the desired lead of the wire coil, and the wire advances in a direction from the smaller-diameter end toward the larger-diameter end of the mandrel. Since the guide means is stationary, it pushes successively formed convolutions axially of the rotating mandrel, i.e., toward and beyond the larger-diameter end of the conical peripheral surface.
Apparatus of the above outlined type are disclosed in a large number of patents and other printed publications. Reference may be had to German Pat. Nos. 337,096, 362,058 and 1,944,371. German Offenlegungsschriften Nos. 2,234,633 and 2,835,511 as well as U.S. Pat. Nos. 3,101,750, 3,378,045, 3,520,334 and 3,568,728. All of these apparatus share the feature that the mandrel has an elongated conical peripheral surface, i.e., that the entire coiling station is adjacent to a surface diverging in the direction of axial movement of the developing coil. The helical path along which the wire advances in the region of the conical external surface of the mandrel is defined by stationary guide means in the form of a sleeve having a helical internal groove or in the form of several rows of pin-shaped guide elements which are staggered with reference to each other to define a helical path of desired lead. It is also known to employ guide means in the form of or including ball bearings. As the wire advances along the helical path, it is expanded by the conical surface of the rotating mandrel and thus undergoes permanent deformation as a result of stretching action upon the material of the wire. In order to reduce friction between the expanding wire and the surface of the mandrel, the apparatus normally comprises means for spraying boring liquid or another suitable lubricant onto the external surface of the wire in a region immediately upstream of the locus of initial contact between successive increments of the wire and the conical surface of the mandrel. It has been found that such lubrication is of little help or to no avail at all because the friction-induced heat is often so pronounced that the lubricant evaporates on contact with the conical surface. Frictional engagement between the wire and the mandrel then entails a deterioration of the external surface of the coiled product.
Another drawback of presently known apparatus is that the convolutions of the freshly finished coil do not remain in axial alignment with the mandrel. In other words, the axes of those convolutions which advance beyond the larger-diameter end of the mandrel are likely to be inclined with reference to the axis of the mandrel so that it is difficult to properly guide the coil in a machine which forms spiral binders and threads the binders into the perforations of successively supplied stacks of paper sheets or the like. The absence of axial alignment between the mandrel and the convolutions which have advanced beyond the larger-diameter end of the mandrel is attributable to the tendency of such convolutions to contract as soon as they leave the conical surface. The inclination of that portion of the coil which has advanced beyond the mandrel with reference to the axis of the mandrel depends on the lead of the coil, i.e., it varies from one type of coil to another type so that it is necessary to carry out prolonged adjustments whenever the apparatus is converted from the making of one type of coil to the production of a different type of coils. As a rule, accurate adjustment (e.g., so that the coil can be threaded into the rows of perforations in successive stacks or piles of sheets) is achieved only after several attempts, i.e., each adjustment takes up a substantial amount of time and must be carried out by skilled, experienced and careful attendants.